The Boeing XPBB-1 Sea Ranger was a prototype twin-engined flying boat Patrol Bomber built for the United States Navy. The order for this aircraft was cancelled to free production capacity to build the Boeing B-29, and only a single prototype was completed.

Photos of the Boeing XPBB-1 "Sea Ranger"
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Recognizing its mission in the vast expanses of the Pacific Ocean and that Japan might be an enemy, the US Navy started a program in the late 1930s to develop a long-range flying boat. The Model 344 design offered by Boeing was chosen, and a contract for 57 aircraft was awarded in June 1940. The designation given to the type was PBB for "Patrol Bomber, Boeing". The defensive armament was five powered turrets equipped with 50 caliber machine guns, installed in the nose, tail, upper fuselage, and in two waist positions. Offensive armament could consist of up to 20,000 lb of bombs or two torpedoes.

Normal range using the main (1565 US gal) and inboard (1250 US gal) fuel tanks was 4245 miles. The 1710 US gallon auxiliary fuel tanks were intended to be used only in an overload condition, in which the PBB would use catapult-assisted take off to achieve a theoretical range of 11000 miles. Eventually, the catapult launce was discarded in favor of jet- or rocket- assisted takeoff.

The prototype, designated XPBB-1, made its first flight in July 1943; it handled very well and was considered technically successful. However, the need for a long-range flying boat had been reduced by the ability of land planes such as the Consolidated PB4Y to fly long-range missions over the ocean. The construction of the PBB was deemed to have a negative impact on the production rate of the B-29. Thus, the PBB program was cancelled. The single XPBB-1 was handed over to US Navy, and was used in trials programmes until 1947, when it was finally retired. As the single example of the type, it earned the nickname "Lone Ranger".